An earth boring bit of the type concerned herein has a bit body with three depending bit legs. A rolling cone or cutter is rotatably mounted to each bit leg. Each cone comprises a steel shell having a plurality of rows of milled teeth formed in the cutter shell by machining. To reduce wear, the teeth and gage surface are hardfaced with a hardfacing that is typically tungsten carbide in an alloy steel matrix. Also, it is known to place hardfacing at the spear point area of the cone. The remaining portions of the cones are left free of hardfacing in the prior art.
While drilling, particularly in unconsolidated, highly abrasive sand formations, the cutting structure and cone shell are subjected to the abrasive cuttings being drilled, the high sand content in the mud, and the sand particles that remain on the borehole bottom due to poor rig hydraulics and/or horizontal drilling. All of these factors cause wear on the teeth and erosion on the shell of the cones. Even if the drilling flow rate or rig hydraulics is high enough to flush sand particles from the borehole bottom, the high flow rate of the mud discharged through the nozzles can cause the teeth and cone shell to be eroded prematurely.
Many operators use center-jet nozzles to help with the cone cleaning. This constant impingement of abrasive drilling fluid exiting the center-jet nozzles can cause abrasive and erosive wear that will substantially damage the base of the teeth and cone shell. This damage will undermine the individual teeth and eventually may cause them to break off. The hardfacing protection of the prior art only offers partial reduction of abrasive and erosive wear.